In attempts to reduce the size and cost of accelerometers, many different types of acceleration sensing structures have been devised. These structures include capacitive devices and piezoresitive devices, some of which are constructed using semiconductor manufacturing techniques and/or bulk micromachining. The capacitive devices generally consist of a conductive plate, formed of metal or the like, which is mounted on a substrate for movement relative thereto. The plate is positioned parallel to a planar surface of the substrate and forms one or more capacitances therewith. When the plate moves, due to an acceleration force thereon, the capacitances change. This change is sensed by connected electronic circuits and converted to a signal representative of the acceleration.
Accelerometers are useful in inertial guidance systems to sense movement, or acceleration, of a vehicle in all directions. From this information the position of the vehicle can be determined at all times. Accelerometers, such as those described above, are manufactured as a single axis device. To obtain an indication of movement in all directions, three of the prior art accelerometers must be positioned so that the sensitive axes are mutually orthogonal. This means that the final package is still relatively large since one or more of the accelerometers must be positioned at an angle to the others and the entire package can never be formed as a single planar package. Further, since each accelerometer is constructed on a separate semiconductor substrate, signals must be communicated between chips. It is a well known fact that large amounts of power are required to amplify, buffer and communicate signals between chips.